1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, relates to a semiconductor device using a lead frame as a wiring base member and a manufacturing method thereof.
2. Description of the Background Art
Under the background of high density integration of semiconductor chins, it has been increasingly popular to use a ball grid array (hereinafter referred to as BGA) type semiconductor device in which an external lead is arranged over a surface. Generally, in the BGA type semiconductor device, a printed circuit board as a wiring base is popularly used. Since such a convention BGA type semiconductor device is, however, high-priced, a BGA type semiconductor device using a low-priced lead frame as a wiring base member has been practically used.
A semiconductor device using a conventional lead frame as a wiring base member is hereinafter described with reference to the accompanying drawings. FIG. 11A is a sectional view showing a construction of a conventional BGA type semiconductor device disclosed in the Japanese Laid-Open Patent Publication (unexamined) No. Hei 11-74404, and FIG. 11B is a bottom view of the semiconductor device shown in FIG. 11A. FIG. 12A is a plan view showing a lead frame used in the convention BGA type semiconductor device and arranged in a single line. FIG. 12B is a sectional view taken along the line XIIbxe2x80x94XIIb indicated by the arrows in FIG. 12A. FIG. 12C is a sectional view taken along the line XIIcxe2x80x94XIIc indicated by the arrows in FIG. 12A.
In FIGS. 11A, 11B, 12A, 12B and 12C, the conventional BGA type semiconductor device uses a lead frame 50 as a wiring base member, and a semiconductor chip 1 provided with a pad electrode is mounted on a die pad 2 with a junction material 3. The semiconductor device has solder ball mounting portion (hereinafter referred to as external electrode portion) 4. A lead electrode 5, of which an inside end portion is radially arranged the die pad 2, and a pad electrode of the semiconductor chip 1 are connected to each other through a connection lead 6 and sealed with a resin layer 7. Portions 4a and 4b continued underneath the lead electrode 5 are made thin by etching except the external electrode portion 4. Accordingly, the die pad 2, the external electrode portion 4 and a suspension lead 8 for supporting the die pad 2 are exposed on the same surface as the under surface of the seal resin layer 7. A solder ball 9 is mounted on the external electrode portion 4, and an end of the lead electrode 5 and that of the suspension lead 8 are finally cut along the resin seal line 7a. 
A manufacturing method is hereinafter described with reference to FIGS. 11 to 13. FIGS. 13A, 13B and 13C are explanatory views showing a manufacturing method of the conventional BGA type semiconductor device. FIG. 13A is a sectional view of the lead frame shown in FIG. 12C. FIG. 13B is a sectional view showing molds applied at the time of sealing with the seal resin layer. FIG. 13C is a sectional view showing an assembling step before mounting of the soldering ball has been completed.
First, the lead frame 50 shown in FIGS. 12A, 12B and 12C is manufactured. More specifically, after forming a resist film on the upper surface 50a and the under surface 50b of the lead frame 50 and patterning it, as shown in FIG. 12A the lead frame is etched from the upper surface 50a and the under surface 50b. Thus, the die pad 2, the external electrode portion 4, the lead electrode 5, the suspension lead 8 and a dam bar 50c are formed to continue across openings 50d and 50e. Then, after forming a resist film on the under surface 50b of the lead frame 50, except the portions 4a and 4b on the underside of the lead electrode 5, the portions 4a and 4b are formed by half etching.
Subsequently, the semiconductor chip 1 provided with the pad electrode is mounted on the die pad 2 by applying the junction material 3. The pad electrode of the semiconductor chip 1 and the inside end of the electrode 5 are then connected through the connection lead 6. Then, as shown in FIG. 13B, after mounting a lower mold 10 in contact with the die pad 2 and the external electrode portion 4, an upper mold 11 is positioned on the resin seal line 7A and mounted on the upper surface of the lead frame 50. After tightening the two molds 10 and 11, the semiconductor chip 1, the die pad 2, the lead electrode 5 and the connecting lead 6 are sealed with the seal resin layer 7 by transfer molding. Thereafter, when removing the upper mold 11 and the lower mold 10, a non lead type semiconductor devices before mounting the solder ball 9, is obtained as shown in FIG. 13C.
Then, by applying a soldering paste to the external electrode portion 4, the solder ball 9 is mounted on the external electrode potion 4. When the lead electrode 5 protruding from the resin sealing line 7a, and the seal resin layer 7 getting into the underside portions 4a and 4b of the lead electrode 5, made thin by half etching, are cut along the resin seal line 7a with a cutter, the conventional BGA type semiconductor device shown in FIGS. 11A and 11B is obtained.
In the mentioned semiconductor device using the conventional lead frame as the wiring base member, since the die pad 2, the external electrode portion 4, the lead electrode 5, the suspension lead 8 and dam bar 50c continue across the openings 50d and 50e, when sealed with the seal resin layer 7 after mounting the two molds 10 and 11, the molten resin, having a low viscosity, also flows into the opening portion 50d. As a result, there has been a problem that the molten resin intrudes into a small space between contact surfaces, where the die pad 2, the external electrode portion 4, the suspension lead 8 are in contact with the lower mold 10, and comes to form a thin resin film (hereinafter referred to as thin burr).
It is certainly possible to prevent the formation of the thin burr between the external electrode portion 4 and the lower mold 10 if a contact pressure between the external electrode portion 4 and the lower mold 10 is large. However, the lead electrode 5 is made thin by etching and supported like a cantilever at a part held between the lower mold 10 and the upper mold 11 at the position of the resin seal line 7a. Therefore, if the external electrode portion 4 is pressed by the lower mold 10, the lead electrode 5 is deformed by the pressure. As a result, it has been heretofore impossible to secure a contact pressure preventing the formation of the thin burr between the external electrode portion 4 and the lower mold 10.
The formation of the thin burr varies depending on the degree of roughness in surface finishing (hereinafter referred to as surface roughness) of the contact surface where the die pad 2 and the external electrode portion 4 are in contact with the lower mold 10. Generally, the thin burr does not adhere to any die or mold having good surface roughness, but adheres to the die pad 2, the external electrode portion 4, etc. having poor surface roughness. Therefore, it is necessary to remove the thin burr adhered, for example, to the external electrode portion 4. To remove the thin burr, hydraulic pressure trimming, chemical trimming, chemical and hydraulic pressure trimming, etc. are performed, and after removing the thin burr, it is necessary to perform treatments such as washing, drying, etc., and as a result manufacturing cost is high.
There has been another problem with the lead electrode 5 protruding from the resin seal line 7a, the seal resin layer 7 gets into the portions 4a and 4b made thin by half etching, and the suspension lead 8, cut using a cutter along the resin seal line 7a. Therefore, it is easy to cause a failure in cutting the portion of the seal resin layer 7 in the portion 4b. As a result, the resin seal line 7a is not linear but has a complicated crushed configuration, resulting in a defective product.
Moreover, as the semiconductor chip 1, the die pad 2, the junction material 3, the lead electrode 5 and the seal resin layer 7 forming the semiconductor device are different in their coefficient of linear expansion, so a curvature is produced due to thermal deformation at the time of manufacturing the semiconductor device.
As a result, there has been a further problem when the non lead type semiconductor device is mounted on an other board, the external electrode portion is inclined and any desirable contact surface is not achieved in the electrical connection with the other board.
The present invention has been made to solve the above-discussed problems and has an object of providing a novel semiconductor device capable of preventing the formation of thin burr on a surface in contact with a lower mold, for example, between a die pad or an external electrode portion and the lower mold.
Another object of the present invention is to provide a novel semiconductor device capable of preventing a cutout portion of a seal resin layer of the semiconductor device from being a complicated crushed configuration.
A further object of the present invention is to provide a novel semiconductor device capable of achieving a desirable contact surface in electrical connection between an external electrode portion and other board at a time of mounting the semiconductor device on the other board, even if a curvature is produced due to thermal deformation of the semiconductor device.
A novel semiconductor device in a first aspect of the invention includes: a semiconductor chip provided with an upper surface and an under surface and having a plurality of pad electrodes; a plurality of lead electrodes arranged corresponding to the plurality of pad electrodes and extending peripherally on the under surface side of the semiconductor chip; connecting means for connection between the plurality of pad electrodes and the plurality of lead electrodes; a seal resin layer for sealing integrally the semiconductor chip, the lead electrodes and the connecting means; in which each of the plurality of lead electrodes includes a thin internal lead portion having a connection part with the connecting means on the upper surface side, and a thick external electrode portion protruding toward the under surface side to form a connection part to outside; the seal resin layer has an underside which forms substantially the same surface as the under surface of the internal lead portion of the lead electrodes, and the external electrode portion protrudes downward from the underside of the seal resin layer.
In the semiconductor device of above construction, since the external electrode portion protrudes downward from the seal resin layer, even if a curvature is produced due to difference in coefficient of thermal expansion of the components of the semiconductor device, it is possible to achieve a desirable contact surface in the electrical connection between the external electrode portion and other board.
It is preferable that the semiconductor device includes: a semiconductor chip provided with an upper surface and an under surface and having a plurality of pad electrodes; a plurality of lead electrodes arranged corresponding to the plurality of pad electrodes and extending peripherally on the under surface side of the semiconductor chip; connecting means for connection between the plurality of pad electrodes and the plurality of lead electrodes; an auxiliary electrode provided around the plurality of lead electrodes; a seal resin layer for sealing integrally the semiconductor chip, the lead electrodes, the connecting means and the auxiliary electrode; in which each of the plurality of lead electrodes includes a thin internal lead portion having a connection part with the connecting means on the upper surface side, and a thick external electrode portion protruding toward the under surface side to form a connection part to outside; the seal resin layer has an underside which forms substantially the same surface as the under surface of the internal lead portion of the lead electrodes and the auxiliary electrode, and the external electrode portion protrudes downward from the underside of the seal resin layer.
In the semiconductor device of above construction, since the external electrode portion protrudes downward from the seal resin layer, even if a curvature is produced due to difference in coefficient of thermal expansion of the components of the semiconductor device, it is possible to achieve a desirable contact surface in the electrical connection between the external electrode portion and any other board.
A method of manufacturing a semiconductor device in a second aspect of the invention includes the steps of: using a lead frame composed of a plate-like body having an uneven upper surface and a plain under surface, the plate-like body including a first thin portion for mounting a semiconductor chip provided with a plurality of pad electrodes, a plurality of first thick portions provided around the first thin portion for forming lead electrodes respectively arranged corresponding to the pad electrodes of the semiconductor chip, a second thin portion provided between the plurality of first thick portions, a third thin portion provided for surrounding the plurality of first thick portions, and a second thick portion provided around the third thin portion; sealing integrally the semiconductor chip, the lead electrodes and connecting means up to the same surface as that of all thin portions with a seal resin layer, after making a connection between the plurality of pad electrodes of the semiconductor chip mounted on the first thin portion and the plurality of lead electrodes by the connecting means; and removing the first, second and third thin portions by etching so that each of the plurality of lead electrodes includes a thin internal lead portion having a connection part to the connecting means on the upper surface side and a thick external electrode portion protruding toward the under surface and forming a connection part to outside; in which the seal resin layer is formed so that the underside thereof forms substantially the same surface as the under surface of the internal lead portion of the lead electrodes, and that the external electrode portion protrudes downward from the underside of the seal resin layer.
In the semiconductor device manufactured as described above, since the external electrode portion protrudes downward from the seal resin layer, even if a curvature is produced due to difference in coefficient of thermal expansion of the components of the semiconductor device, it is possible to achieve a desirable contact surface in the electrical connection between the external electrode portion and other board.
It is also possible to form a concave part on the upper surface of the lead frame in the first, second and third thin portions. By removing the first, second and third thin portions by etching, the peripheral portion of the concave part lies in a line with the peripheral portion of the semiconductor device including the semiconductor chip, lead electrodes, seal resin layer, etc. provided in the concave part. Under such a condition, by pushing the semiconductor device from the under surface side of the lead frame, it is possible to separate easily the lead frame from the semiconductor device without using any cutter. It is further possible to prevent the separated portion between the lead frame and the semiconductor device from being a complicated crushed configuration.
It is preferable that the first, second and third thin portions have substantially the same thickness. As a result of such construction, the under surface side of the lead frame can be formed into an integrated one component over the first, second and third thin portions. Therefore, the under surface side of the lead frame comes in full contact with a lower mold. When sealing with the seal resin layer, the seal resin layer is shut off by the first, second and third thin portions. Consequently, there is no seal resin layer flowing in the portion where the under surface of the lead frame and the lower mold are in contact with each other, and it is possible to prevent the formation of thin burr.
It is further preferable that the method of manufacturing a semiconductor device includes the steps of: using a lead frame composed of a plate-like body having an uneven upper surface and a plain under surface, the plate-like body including a first thin portion for mounting a semiconductor chip provided with a plurality of pad electrodes, a plurality of first thick portions provided around the first thin portion for forming lead electrodes respectively arranged corresponding to the pad electrodes of the semiconductor chip, a second thin portion provided between the plurality of first thick portions, a third thin portion provided for surrounding the plurality of first thick portions, a second thick portion provided around the third thin portion to form an auxiliary electrode, a fourth thin portion provided around the second thick portion, and a third thick portion provided around the fourth thin portion; sealing integrally the semiconductor chip, the lead electrodes, the connecting means and the auxiliary electrode up to the same surface as that of all of the thin portions with a seal resin layer, after making a connection between the plurality of pad electrodes of the semiconductor chip mounted on the first thin portion and the plurality of lead electrodes by the connecting means and making a connection between the lead electrodes and the auxiliary electrode; and removing the first, second, third and fourth thin portions by etching so that each of the plurality of lead electrodes includes a thin internal lead portion having a connection part to the connecting means on the upper surface side and a thick external electrode portion protruding toward the under surface and forming a connection part to outside; in which the seal resin layer is formed so that the underside thereof forms substantially the same surface as the under surface of the internal lead portion of the lead electrodes and the auxiliary electrode, and that the external electrode portion protrudes downward from the underside of the seal resin layer.
In the semiconductor device manufactured as described above, since the external electrode portion protrudes downward from the seal resin layer, even if a curvature is produced due to difference in coefficient of thermal expansion of the components of the semiconductor device, it is possible to achieve a desirable contact surface in the electrical connection between the external electrode portion and other board.
It is also possible to form a concave part on the upper surface of the lead frame in the first, second and third thin portions, and to arrange the second thick portion provided to form the auxiliary electrode around the concave part. By removing the first, second, third and fourth thin portions by etching, the semiconductor device including the semiconductor chip, lead electrodes, seal resin layer, etc. provided in the concave part is separated from the lead frame at the peripheral portion of the semiconductor device. As a result, it is possible to separate inevitably the lead frame from the semiconductor device without using any cutter. It is further possible to prevent the separated portion between the lead frame and the semiconductor device from being a complicated crushed configuration.
It is further preferable that the first, second, third and fourth thin portions have substantially the same thickness. As a result of such construction, the under surface side of the lead frame can be formed into an integrated one component over the first, second, third and fourth thin portions. Accordingly, in the manufacture of the semiconductor device using the lead frame as a wiring base member, the under surface side of the lead frame can be formed into an integrated one component over the first, second, third and fourth thin portions. Therefore, in the manufacture of the semiconductor device using the lead frame as a wiring base member, the under surface side of the lead frame comes in full contact with a lower mold and seals with the seal resin layer. When sealing With resin layer is shut off by the first, second, third and fourth thin portions. Consequently, there is no seal resin layer flowing in the portion where the under surface of the lead frame and the lower mold are in contact with each other, and it is possible to prevent the formation of thin burr.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.